1. Field of the Invention
The present invention relates to a thermal management system for a vehicle.
2. Background Art
In response to demands for improved fuel economy and reduced emissions, vehicles today are being manufactured with systems designed to increase combustion efficiency and reduce exhaust emissions. One way to reduce exhaust emissions, particularly in diesel engines, is to introduce some of the engine exhaust gas back into the combustion cylinders to lower the temperature of combustion. These systems, known as exhaust gas recirculation (EGR) systems can be particularly useful in reducing emissions of nitrogen-oxygen compounds, known collectively as NOx.
A number of EGR systems are described in a Society of Automotive Engineers (SAE) Technical Paper, Document Number 2001-01-1732, entitled “Thermal Management Evolution and Controlled Coolant Flow,” copyright 2001. One such system includes a controllable electric pump for circulating engine coolant through an EGR cooler. The electric pump can replace a larger, mechanical pump, thereby providing an overall space savings. Another system described in the SAE paper includes a separate EGR cooling loop having its own coolant loop separate from the engine coolant loop. The EGR cooling loop includes a controllable electric pump, and its own liquid-to-air heat exchanger for dissipating heat from the EGR coolant.
Although EGR systems used on vehicles today may be helpful to reduce the temperature of combustion in the engine cylinders, they may not provide a high degree of control over the temperature of the combustion. In addition, passing hot exhaust gas through control valves, such as an EGR valve, can be damaging to the valve. Therefore, it would be desirable to provide a thermal management system for a vehicle that included exhaust gas recirculation and provided a high degree of control over the temperature of the air entering the engine cylinders, thereby controlling the temperature of combustion to reduce exhaust emissions.